An innovative way to enhance the high temperature properties of alkali activated cement mortars prepared by using glass powder as precursor

This paper presents an innovative way of enhancing the residual strength and the dimensional stability after elevated temperature exposures for Alkali Activated Cement (AAC) mortar prepared with recycled glass materials as the principle precursor and fine aggregate. The reference AAC mixture was prepared with Glass Powder (GP) solely as the precursor material. A 28-day compressive strength of slightly over 10 MPa was attained but the samples experienced severe dimensional instability (expansion) after 2 h of exposure to 800 °C. To address this problem, 10% to 25% calcium aluminate cement (CAC) was used to replace the GP and the expansion was effectively controlled when the amount of CAC reached 15%. Also, significant strength increment was attained after the elevated temperature resistance test. The severe expansion of the reference mortar was attributed to the density reduction and volume expansion of the recycled glass materials at the elevated temperature and an extremely porous structure (porosity of over 50%) was resulted after the test. Meanwhile, for the CAC incorporated mixtures, the dehydration of sodium aluminum silicate hydrate at temperature ranging from 250–270 °C enabled sufficient space to accommodate the glass materials expansion. The results show that with the incorporation of CAC, recycled glass dominated AAC mortars that contain higher than 80% total recycled glass materials can be fabricated. A residual strength increment of up to 450% can be obtained while maintaining the original dimension without expansion after the elevated temperature exposure.